1. Field of the Invention
The invention relates to an axially compact design of a gearbox.
2. Description of Related Art
Typically, gearboxes are used to increase torque while reducing the speed of a prime mover output shaft (e.g. a motor drive shaft). This means that the output shaft of a gearbox will rotate at a slower rate than an input shaft. This reduction in speed will produce a mechanical advantage, causing an increase in torque. Alternatively, gearboxes can be setup to do the opposite and provide an increase in shaft speed with a reduction of torque. Some of the simplest gearboxes merely change the physical direction in which power is transmitted.
Due to the shrinking size of automotive vehicles and increasing fuel economy standards, size and weight of major vehicle components is of critical importance. Gearboxes used in a vehicle driveline are usually large and bulky. Thus, reducing the size and weight of such gearboxes is highly desirable.
Conventional gearbox designs include a housing for containing a gear having a gear portion and an axially extending gear stem. The gear is supported by a pair of spaced apart bearings disposed radially between the gear stem and the housing. The gear stem includes an end portion spaced apart from the gear portion that is externally splined for engagement with an output member having an output flange and an axially extending output stem that is internally splined. The gear stem extends through the output stem and a clamping nut is threaded to the end portion of the gear stem to retain the output member and gear together. Thus, in conventional gearbox designs, the axial length of the gearbox housing is generally determined by the axial length of the gear and output member.
In order to reduce the axial length of the gearbox housing, the axially extending gear stem may be shortened and splined along its length. The axially extending output stem, which is internally splined, overlaps and engages with the externally splined gear stem. The spaced apart bearings are thus disposed radially between the output stem and the housing.
There are certain disadvantages with known gearbox designs. First, the clamping nut positioned outside of the housing adds to the axial length of the gearbox. Second, two separate leak paths for gearbox lubricant exist at the end of the housing adjacent the output flange. A first leak path exists between the output flange and the housing. A second leak path exists at the interface between the clamping nut, the gear stem and the output flange. Third, the thrust face of the clamping nut is seated against the output flange, which is not a hardened material or must be hardened for this purpose. Fourth, the clamping nut is sometimes required to be staked to the gear stem to keep the clamping nut from coming loose. Staking the clamping nut to the hardened gear steel of the gear stem may result in a less than robust joint. If disassembly of the clamping nut and gear stem is required and the gear is to be re-used, there is potential for residual damage to the gear stem from the previous staking operation. In addition, shock load from the staking operation is transmitted through the brittle gear steel. Fifth, after carburizing the gear, the end of the gear stem that is threaded to receive the clamping nut becomes brittle and must be annealed to prevent fracture.
It is desirable, therefore, to provide an improved, axially compact gearbox that reduces the number of leak paths for gearbox lubricant. It is also desirable to provide an axially compact gearbox that is more robust, while being cheaper and easier to manufacture.